Just today Twitter gave me a recommendation to follow Joe Armstrong.
I know that they don't know that he's deceased, but simultaneously their impeding policy on clearing out old accounts will hit the same problem, and I'm not entirely sure that they'll be up for it and whether they'll do a good enough job. Sure, the one-tweet-years-ago accounts can go, yet Twitter is in a peculiar position if they want to free up username real-estate.
YouTube deals with this by removing channels whose account hasn't been logged into for four years, I believe. (That's how we (I?) lost ReverseMan. [The channel, not some weird video.])